The structure of these tires, in fact, accumulated--under the effect of an imposed deformation--elastic energy which was given back almost instantaneously upon termination of the stress, amplifying the unevennesses transmitted by the road surface layer, with ensuing stability loss of the vehicle.
In particular, during the straightaway running such excessive stiffness causes, at low speeds, high frequency (8-10 Hz) oscillations on the front tire (shimmy effect), causing driving to be precarious.
To try to obviate these problems, it has recently been proposed in U.S. Pat. No. 5,975,175, the use of a radial-ply tire provided with a belt structure comprising circumferentially-oriented cords, preferably metal cords, also indicated by the term: zero-degree cords.
This type of tire has unquestionably improved the situation in terms of comfort and driving stability: in fact, the oscillations of the vehicle at straightaway high speeds have disappeared and in particularly the shimmy effect has been substantially eliminated.
However, even if improvements as to the comfort and reduction of the driver's weariness have been achieved, the tires of the aforesaid type have not allowed, at least so far, neither to improve the wet grip of the vehicle nor to increase the wear resistance and, consequently, the kilometric yield of the tread band.